The objectives of this research are to prepare reconstituted membranes that satisfy two conditions: (1) The membranes must be immunologically functional in the sense that they mimic natural biological membranes in their interactions with both afferent and efferent components of the immune system. (2) The membranes must be chemically defined and have measureable physical properties, especially lateral distribution and motion of membrane components. Reconstituted membrane functions of particular interest include susceptibility to cytolysis by antibody-dependent macrophages, and by virus/hapten specific, H-2 restricted cytotoxic T cells. Also included are studies of membrane-mediated conformation changes in antibodies bound to lipid haptens, the kinetics of antibody-dependent activation of Cl, neutrophils, and macrophages, as well as the stimulation of B cells by lipid membranes containing a specific mitogenic lipoprotein and lipid hapten. Periodic pattern photobleaching methods will be used to study the lateral diffusion and interactions of several viral proteins and H-2 molecules in reconstituted membranes, and cellular membranes. In all cases emphasis is placed on the molecular events required for cell-cell recognition and triggering.